Introduction of Cement

Introduction of Cement: Cement means ‘any substance that acts as a binding agent for different materials ‘. Cement, in engineering field and especially in construction industry, is a material, which is produced by calcining at high temperature (1400°C) an intimate mixture of calcareous, siliceous and aluminous substances and crushing the resulting clinkers to a fine powder.

Function of Cement in Concrete

When cement is mixed with water, it forms a paste, which hardens and binds the aggregate (sand, gravel) together to form a hard durable mass called concrete. Thus, cement is one of the important ingredients of concrete.

Chemical Ingredients of Cement

The chemical Ingredients of cement are:

Lime (CaO),
Silica (SiO),
Alumina (Al2O3),
Iron oxide (Fe2O3)

Chemical Compounds of Cement

The main chemical compounds of cement are:

Tri-calcium Silicate,
Di-calcium Silicate,
Tri-Calcium Aluminate,
Tetra-calcium Aluminium Ferrite,
Free Lime,
Gypsum

Chemical Constituents of Ordinary Portland Cement (OPC)

The raw materials used for manufacturer of cement consists mainly of Silica, Lime and Alumina, Iron oxide, Sulphur trioxide and other alkalies are also present but in very small proportions.
These materials are intimately mixed and burnt at a temperature of about 1400°C in a klin to form clinkers which are complex chemical compounds.
The relative proportions of these oxides are responsible for affecting the various properties of cement.
The chief chemical ingredients and their proportions, in any ordinary portland cement, are given below.

Compounds Percentage

Lime 60 to 67%

Silica 17 to 25%

Iron oxide or Ferrous oxide 0.5 to 0.6%

Alumina 3 to 8%

Gypsum or Calcium sulphate 3 to 4%

Magnesium oxide 0.1 to 4%

Sulphur trioxide 1 to 3%

Alkalies such as Soda and Potash 0.1 to 1%

Compounds Formula

Lime CaO

Silica SiO2

Iron oxide or Ferrous oxide Fe3O3

Alumina Al2O3

Gypsum or Calcium sulphate CaSO4

Magnesium oxide MgO

Sulphur trioxide SO3

Alkalies such as Soda and Potash Na2O, K2O

Bogue’s Compounds

The raw materials, when subjected to high temperature, combine with each other to form complex compounds. The four compounds usually regarded as majour compounds. These compounds are in anhydrous state (i.e. without any water molecules in their chemical formula).

Compounds Percentage

Tri-calcium Silicate 21 to 46%

Di-calcium Silicate 25 to 50%

Tri-Calcium Aluminate 5 to 11%

Tetra-calcium Aluminium Ferrite 9 to 14%

Other constituents and Gypsum 80%

Compounds Formula

Tri-calcium Silicate 2(CaO) SiO2

Di-calcium Silicate 3(CaO) SiO2

Tri-Calcium Aluminate 3(CaO) Al2O3

Tetra-calcium 4(CaO)

Aluminium Ferrite Al2O3 Fe2O3

Other constituents and Gypsum

Introduction of Cement